Julian,
I think the key to what anyone's power requirements are is how and where they plan to use their vessel. If you're operating strictly on calm water like lakes and canals, the power requirements are much lower because you can rely on gaining momentum and only need to overcome the hydrodynamic drag of your hull.
However, if you plan on being in any kind of wave action such as open sounds or bays, your power requirements increase and if you're going in the ocean, they become even greater. I think .5 kW/ton or even a little less is fine for calm water operation and will even allow you good control in moderate seas but you might be going slower than you'd like. However if you're going to be in open water a lot, the 1 kW/ton is a better standard.
Your point about the prop is a very good one.
Carter
On Wednesday, March 19, 2014 9:26 AM, Julian Webb <julian.proto@gmail.com> wrote:
i agree
i used the "you need 1/3 the electric power to match any i.c." so as my 13 ton boat had 2 x 53 hp diesels i installed 2 x 15 hp electric motors. i had the props designed to maximise efficiency/speed etc at river/canal speed of 5-10 knots, as i thought it would be a shame to go to all that trouble and expense and ruin it all with lousy props (just like buying a great sound system and finishing it off with lousy speakers).
i would guess i could do with 1 x 15 hp motor most of the time. i have mine on 1/2 speed (1/4 power load near enough) and as i'm not after the fast life it's easily enough.
i have seen some barges and boats 30+ meters long with 1 x 75 -90 hp motors, and they're commercial units carrying freight.
once you get a displacement hull moving ( or any really without getting into an argument over planing/making waves isn't more speed etc) a bit like a train, it takes way less to keep them moving than it did to get it there.
once you get a displacement hull moving ( or any really without getting into an argument over planing/making waves isn't more speed etc) a bit like a train, it takes way less to keep them moving than it did to get it there.
i have really only used full power twice, to get out of the way of some dick head who was out of control. as they were fibreglass and i'm steel maybe i shouldn't have haha.
good luck
On 14 March 2014 08:01, Hannu Venermo <gcode.fi@gmail.com> wrote:
Hear hear !
The old rule was much less Hp per ton, half the figure mentioned.
As you have managed, succesfully, at 0.2 kW/ton, I personally believe
the old rule of (between 1/2 to 1 Hp per ton) is much more appropriate.
Thus somewhere between 300-740 Watts/ton, or about 500W, is likely a
good option.
(10m) Sailboats with 12 Hp auxiliaries manage perfectly well.
Thats about equivalent to a 3-4 kW electric solution.
On 13/03/2014 16:41, Carter Quillen wrote:
> I have been pushing a 20 ton boat with a 7 kiloWatt peak motor,(.35
> kW/ton) that I almost always operate at 4 kiloWatts, (.2 kW/ton) for
> almost a 1000 miles now. It is fair to say it's a bit slower than most
> people would want but it works for me and I've always been able to
> maintain control of my boat, albeit in slow motion sometimes, even in
> some pretty adverse conditions.
--
-hanermo (cnc designs)
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